But you are operating under the assumption that with the introduction of a Canon mirrorless FF camera, that ALL EF lenses will suddenly become obsolete. That assumption is flawed.
Now, before someone brings up the FD to EF transition, EF gave the users AF capabilities. Even if Canon came up with some magic way to AF FD mount lenses, the users were going to have to buy a new body and new AF-FD lenses anyway. They chose to make a clean break and introduced digital communications, which added a lot more than just AF to lenses.... Going from EF to a new mount brings absolutely ZERO new capacities to the new camera system. Huge risk for no gain? I don't think so!
Fourth, Canon has just introduced a whole slew of new Big Whites.... there is the 100-400, the pair OF 70-200'S, and now a 400F2.8 (and another unspecified lens) are on the way. These lenses are expensive to design and it takes many years to recoup the development and production change costs. These are not the actions of a company getting ready to drop a product line!
My bet is that the EF mirrored lines will continue for many years into the future, and that eventually there will some mirrorless EF models introduced (both crop and FF). Parallel to this, there will be a more compact FF mirrorless camera with a few lenses, similar to the M series, but with a few L quality SLOW (F5.6 or 6.3) lenses.